Rotary knife having thin removable cutting edge



April 28, 1953 w. s. KO-EHLER 2,636,562 ROTARY mmmmc MIN-REMOVABLE cu'mnc EDGE Filed Au 13. 1951 Mfnesaes:

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Patented Apr. 28, 1953 ROTARY KNIFE HAVING THIN REMOVABLE CUTTING EDGE Wilhelm F. Koehler, Darmstadt, Germany Application August 13, 1951, Serial No. 241,617 In Germany August 5, 1950 2 Claims. (Cl. 164-70) This invention relates to a rotary knife having thin removable cutting edge. For slitting webs of paper, cardboard, cloth, etc., rotary knives are used of which one or more are mounted on a shaft. The circumference of a plurality of those knives forms a cylindrical surface serving to guide the webs to be slit. Each knife, however, is fitted with a groove, the edge of which meshes with the appertaining counter knife disc. For this slitting process, not only the edge but the entire body of the knife has to be made of high quality material which is very expensive. A further disadvantage results from the following:

Each regrinding widens the grooves and reduces, therefore, the grinding surface of the web. Also, as the width of the grooves simultaneously is also decisive for the observance of the slitting widths, knives can be used only with the same groove widths.

It is necessary, therefore, if only one knife becomes blunt, that all knives mounted on the same shaft must be reground to the same extent. Finally, this regrinding makes the use of a high-quality grinding machine necessary and which is of expensive precision.

The invention removes these disadvantages. It refers to a rotary knife comprising a hub body or member and an annular disc of the same outside diameter as the hub body, a lateral surface of which is pressed against a lateral surface of the hub body.

The manufacture of such annular discs is less expensive than the regrinding of the abovedescribed rotary knives. When the knife becomes blunt, the annular disc, therefore, is exchanged if it is not preferred to utilize it on both sides by reversal. By replacing such annular discs, the change of the groove widths recognized before as disadvantageous, as well as the disadvantageous influence upon the slitting widths, are avoided. Whereas knives of known construction are to be replaced after repeated regrinding, the life of the hub body is practically unlimited.

In order to obtain a perfect contact of the disc on the hub body, it is advantageous to give the unstretched annular disc a plane form. When simultaneously the lateral contact surface of the hub body against which the annular disc is pressed receives a slightly conical form, the two bodies have a close contact on the entire lateral surface. The pressing process of the annular disc against the hub body can be obtained by a nut or the like mounted on the hub part of a smaller diameter, the nut having a diameter smaller than the maximal diameter of the hub body. It is advantageous, for pressing the annular disc, to use a known annular spring disc, the radial elasticity of which will support the annular disc in a groove to be provided on a part of the hub body whereas the axial force of the annular spring disc reacts on the circumference, pressing the annular disc against the hub body. The angle hereby attained at the slitting edge of the annular disc acts advantageously upon the clean out. After the slitting edge has become blunt, the annular disc can be turned so that the edge previously contacting the hub body will now act as the slitting edge. After the wear of both edges, the annual disc is exchanged for a new one.

An example of this invention is shown in the accompanying drawing which shows a crosssectional view.

The hub body I has a part with a larger diameter and an integral and adjacent part with a smaller diameter. Against a conical lateral surface 2 of the hub body the annular disc 3 contacts with its edge 6 under the axial pressure of an annular spring disc 4. This spring is secured in the groove 5 against sliding from the hub body. It may also be possible to make the lateral surface 2 not conical but plane. It is advantageous, however, to give it the form as shown in the drawing, as in this case the annular spring disc 4, by its axial pressure, forces the annular disc 3 into a perfect contact. For exchanging the annular disc 3, the annular spring disc 4, by means of a suitable tool, can be taken off, whereas the fitting of the spring by hand is possible without tools so that only little time is necessary for turning or exchanging the annular disc.

Having now described my invention what I claim is:

l. A rotary knife for slitting webs of paper, cardboard, cloth and the like comprising an annular hub member having a cylindrical part and a further adjacent cylindrical part of a smaller diameter than the first-mentioned cylindrical part with a lateral shoulder surface extending circumferentially between the two cylindrical parts, an annular thin elastic cutting disc having a hole therein corresponding approximately to the diameter of the second-mentioned cylindrical part of the annular hub member and having an outer diameter corresponding approximately to the diameter of the first-mentioned cylindrical part of the annular hub member when the disc is secured in place thereon, said cylindrical part of smaller diameter having an abutment thereon, and an annular spring ring flexible radially and axially and having a hole therein of approximately equal diameter as the second-mentioned cylindrical part of the hub member, said spring ring engaging said abutment of the cylindrical part of smaller diameter, after being radially spread and's'lid over the smaller cylindrical part of the huhmember, thereby pressing inaxial direction against the cutting disc whereby the cutting disc is sprung into engagement with said lateral shoulder between the -twoeylindricalpartsof the hub member.

2. A rotary knife according to claim 1, in which the lateral shoulder surface of -theannular hub is at an angle less than 90 relative to both cylindrical parts.

WILHELM F. KOEHLER.

References Cited in the file of this patent UNITED STATES PATENTS Number I Name Date 2,151,831 Buccicone Mar. 28, 1939 0 2,239,623 Oster Apr. 22, 1941 FOREIGN PATENTS Number Country Date 11549 Great Britain May 19, 1913 62537.7 Germany Feb. 8, 1936 

